Recently, along with a demand to reduce business trip costs and business trip man hours, communication systems (or remote communication systems) carrying out a TV conference using a communication network (or remote communication network) such as the Internet have become widespread. In such a communication system, display data for displaying material data on a screen, image data and/or voice data are transmitted among plural communication terminals (or remote communication terminals), and thus a TV conference is achieved. Further, thanks to recent improvements of broadband environments, it becomes possible to transmit image data of high image quality and voice data of high voice quality. Therefore, it becomes possible to easily determine a situation of another person with whom a TV conference is being conducted, and it becomes possible to improve fullness of mutual understanding achieved by conversation during the TV conference.
Further, since a communication terminal (or remote communication terminal) becomes capable of transmitting and receiving a large amount of display data simultaneously, it becomes possible for each participant of a TV conference to read conference material while determining a situation of another participant, as a result of image data and the display data being displayed from a display device simultaneously (see U.S. Pat. No. 6,760,749).
However, there may be a case where no material is used in a TV conference. In such a case, nothing is displayed at an area prepared for displaying material data on a display device, and an area prepared for displaying image data of a participant of the TV conference is as is in the original state. It is possible to omit the area displaying nothing so that the area displaying image data is widened, and the image data becomes easier to watch. However, for this purpose, the areas on the display device are to be changed by manual operations.
Further, after the area displaying the image data is widened, there may be a case where during the TV conference, it becomes necessary to use material. Also in such a case, the areas on the display device are to be changed to widen the area displaying the material so that the material becomes easy to be seen, and thus, manual operations become necessary again. Such manual operations may be troublesome for the participants who are conducting the TV conference.